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Sokoloff JB, Lau AWC. Theory of the force of friction acting on water chains flowing through carbon nanotubes. Phys Rev E 2023; 107:055101. [PMID: 37329021 DOI: 10.1103/physreve.107.055101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 04/10/2023] [Indexed: 06/18/2023]
Abstract
A simple model for the friction experienced by the one-dimensional water chains that flow through subnanometer diameter carbon nanotubes is studied. The model is based on a lowest order perturbation theory treatment of the friction experienced by the water chains due to the excitation of phonon and electron excitations in both the nanotube and the water chain, as a result of the motion of the chain. On the basis of this model, we are able to demonstrate how the observed flow velocities of water chains through carbon nanotubes of the order of several centimeters per second can be accounted for. If the hydrogen bonds between the water molecules are broken (as would occur if there were an electric field oscillating with a frequency equal to the resonant frequency of the hydrogen bonds present), it is shown that the friction experienced by the water flowing in the tube can be much smaller.
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Affiliation(s)
- J B Sokoloff
- Northeastern University, Boston, Massachusetts 02115, USA
- Florida Atlantic University, 777 Glades Road, Boca Raton, Florida 33431, USA
| | - A W C Lau
- Florida Atlantic University, 777 Glades Road, Boca Raton, Florida 33431, USA
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2
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Feghhi T, Tichy W, Lau AWC. Pulling a harmonically bound particle subjected to Coulombic friction: A nonequilibrium analysis. Phys Rev E 2022; 106:024407. [PMID: 36109884 DOI: 10.1103/physreve.106.024407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 07/27/2022] [Indexed: 06/15/2023]
Abstract
We address the effects of dry friction, which has emerged only recently to play an important role in some biological systems. In particular, we investigate the nonequilibrium dynamics of a mesoscopic particle, bound to a spring being pulled at a definite speed, moving on a surface with dry friction in a noisy environment. We model the dry friction phenomenologically with a term that is proportional to the sign of the velocity, and by means of numerical simulations of a Langevin equation we show that (a) the frictional force scales with the logarithm of the pulling velocity, (b) the probability distribution function of the spatial displacement away from the potential minimum is non-Gaussian, (c) the fluctuation-dissipation theorem is violated as expected, but (d) the work function obeys the stationary fluctuation theorem, with an effective temperature related to the noise of the system.
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Affiliation(s)
- T Feghhi
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
| | - W Tichy
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
| | - A W C Lau
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
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3
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Feghhi T, Hernandez RX, Stawarski M, Thomas CI, Kamasawa N, Lau AWC, Macleod GT. Computational modeling predicts ephemeral acidic microdomains in the glutamatergic synaptic cleft. Biophys J 2021; 120:5575-5591. [PMID: 34774503 DOI: 10.1016/j.bpj.2021.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 10/21/2021] [Accepted: 11/05/2021] [Indexed: 10/19/2022] Open
Abstract
At chemical synapses, synaptic vesicles release their acidic contents into the cleft, leading to the expectation that the cleft should acidify. However, fluorescent pH probes targeted to the cleft of conventional glutamatergic synapses in both fruit flies and mice reveal cleft alkalinization rather than acidification. Here, using a reaction-diffusion scheme, we modeled pH dynamics at the Drosophila neuromuscular junction as glutamate, ATP, and protons (H+) were released into the cleft. The model incorporates bicarbonate and phosphate buffering systems as well as plasma membrane calcium-ATPase activity and predicts substantial cleft acidification but only for fractions of a millisecond after neurotransmitter release. Thereafter, the cleft rapidly alkalinizes and remains alkaline for over 100 ms because the plasma membrane calcium-ATPase removes H+ from the cleft in exchange for calcium ions from adjacent pre- and postsynaptic compartments, thus recapitulating the empirical data. The extent of synaptic vesicle loading and time course of exocytosis have little influence on the magnitude of acidification. Phosphate but not bicarbonate buffering is effective at suppressing the magnitude and time course of the acid spike, whereas both buffering systems are effective at suppressing cleft alkalinization. The small volume of the cleft levies a powerful influence on the magnitude of alkalinization and its time course. Structural features that open the cleft to adjacent spaces appear to be essential for alleviating the extent of pH transients accompanying neurotransmission.
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Affiliation(s)
- Touhid Feghhi
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Roberto X Hernandez
- Integrative Biology & Neuroscience Graduate Program, Florida Atlantic University, Boca Raton, Florida; International Max Planck Research School for Brain and Behavior, Jupiter, Florida; Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida
| | - Michal Stawarski
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida
| | - Connon I Thomas
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - Naomi Kamasawa
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - A W C Lau
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Gregory T Macleod
- Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida; Wilkes Honors College, Florida Atlantic University, Jupiter, Florida; Brain Institute, Florida Atlantic University, Jupiter, Florida; Institute for Human Health & Disease Intervention, Florida Atlantic University, Jupiter, Florida.
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Feghhi T, Tichy W, Lau AWC. Coulombic Friction between Two Sliding Bio-Filaments: A Computational Model. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.2186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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5
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Lau AWC, Sokoloff JB. Enhancement of the ion concentration in a salt solution near a wall due to electrical image potentials and enhancement of surface tension due to the presence of salt. Phys Rev E 2020; 102:052606. [PMID: 33327151 DOI: 10.1103/physreve.102.052606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 10/23/2020] [Indexed: 06/12/2023]
Abstract
Effects of electrical image potentials on the salt ion concentration near a solid wall are studied using a one-loop approximation treatment of the grand canonical partition function, which is the Debye-Hückel approximation. Electrical image potentials resulting from both metallic and dielectric walls of dielectric constant larger than that of water near the wall are considered. Our treatment of this problem supports the conclusions of an earlier publication by one of the authors which shows that near a solid wall there should be a high concentration of ions, resulting from image potentials. We have also applied our treatment to the increase of the surface tension of a liquid that occurs when salt is dissolved in the liquid. Our treatment gives the -c_{s}log(c_{s}) dependence of the surface tension found by Onsager and Samarasa in the small c_{s} limit, where c_{s} is the salt concentration.
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Affiliation(s)
- A W C Lau
- Physics Department, Florida Atlantic University, Boca Raton, Florida 33431, USA
| | - J B Sokoloff
- Physics Department, Florida Atlantic University, Boca Raton, Florida 33431, USA
- Physics Department, Northeastern University, Boston, Massachusetts 02115, USA
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6
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Acharya P, Lau AWC. Charge regulation of a surface immersed in an electrolyte solution. Eur Phys J E Soft Matter 2020; 43:54. [PMID: 32794084 DOI: 10.1140/epje/i2020-11978-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 07/15/2020] [Indexed: 06/11/2023]
Abstract
In this paper, we investigate theoretically a model of charge regulation of a single charged planar surface immersed in an aqueous electrolyte solution. Assuming that the adsorbed ions are mobile in the charged plane, we formulate a field theory of charge regulation where the numbers of adsorbed ions can be determined consistently by equating the chemical potentials of the adsorbed ions to that of the ions in the bulk. We analyze the mean-field treatment of the model for electrolyte of arbitrary valences, and then beyond, where correlation effects are systematically taken into account in a loop expansion. In particular, we compute exactly various one-loop quantities, including electrostatic potentials, ion distributions, and chemical potentials, not only for symmetric (1, 1) electrolyte but also for asymmetric (2, 1) electrolyte, and make use of these quantities to address charge regulation at the one-loop level. We find that correlation effects give rise to various phase transitions in the adsorption of ions, and present phase diagrams for (1, 1) and (2, 1) electrolytes, whose distinct behaviors suggest that charge regulation, at the one-loop level, is no longer universal but depends crucially on the valency of the ions.
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Affiliation(s)
- P Acharya
- Department of Physics, Florida Atlantic University, 33431, Boca Raton, FL, USA
| | - A W C Lau
- Department of Physics, Florida Atlantic University, 33431, Boca Raton, FL, USA.
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Chen KB, Lau AWC, Orellana-Barrios MA, Pang W. Iatrogenic thoracoscopic right ventricular laceration resulting in cardiovascular collapse treated with extracorporeal membrane oxygenation. J Cardiothorac Vasc Anesth 2011; 26:98-100. [PMID: 21296001 DOI: 10.1053/j.jvca.2010.12.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Indexed: 11/11/2022]
Affiliation(s)
- Kuen-Bao Chen
- Department of Anesthesia, Pain Service and Critical Care Medicine, China Medical University Hospital, Taichung, Taiwan
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Lau AWC, Chen CC, Wu RSC, Poon KS. Hypothermia as a cause of coagulopathy during hepatectomy. ACTA ACUST UNITED AC 2010; 48:103-6. [PMID: 20643371 DOI: 10.1016/s1875-4597(10)60023-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 07/22/2009] [Accepted: 07/27/2009] [Indexed: 12/21/2022]
Abstract
We report a 27-year-old hemostatically competent female scheduled for partial hepatectomy. During the operation, she experienced an accidental inferior vena cava tear and suffered acute blood loss. After fluid resuscitation and blood transfusion, she developed hypothermia, with a temperature of 33.8 degrees C, and severe coagulopathy with activated clotting time exceeding 1500 seconds measured using the Hemochron Response system (ITC, Edison, NJ, USA). Despite sufficient blood transfusion and correction of her electrolyte imbalance, the poor hemostasis persisted. After per-forming peritoneal lavage with warm saline, her condition dramatically improved and her hypothermia and severe coagulopathy were reversed.
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Affiliation(s)
- Albert Wai-Cheung Lau
- Department of Anesthesia, Pain Service and Critical Care Medicine, China Medical University Hospital, Taichung, Taiwan, R.O.C
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Lau AWC, Lubensky TC. Fluctuating hydrodynamics and microrheology of a dilute suspension of swimming bacteria. Phys Rev E Stat Nonlin Soft Matter Phys 2009; 80:011917. [PMID: 19658739 DOI: 10.1103/physreve.80.011917] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Indexed: 05/28/2023]
Abstract
A bacterial bath is a model active system consisting of a population of rodlike motile or self-propelled bacteria suspended in a fluid environment. This system can be viewed as an active, nonequilibrium version of a lyotropic liquid crystal or as a generalization of a driven diffusive system. We derive a set of phenomenological equations, which include the effects of internal force generators in the bacteria, describing the hydrodynamic flow, orientational dynamics of the bacteria, and fluctuations induced by both thermal and nonthermal noises. These equations violate the fluctuation dissipation theorem and the Onsager reciprocity relations. We use them to provide a quantitative account of results from recent microrheological experiments on bacterial baths.
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Affiliation(s)
- A W C Lau
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
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Lacoste D, Lau AWC, Mallick K. Fluctuation theorem and large deviation function for a solvable model of a molecular motor. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 78:011915. [PMID: 18763990 DOI: 10.1103/physreve.78.011915] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 04/25/2008] [Indexed: 05/26/2023]
Abstract
We study a discrete stochastic model of a molecular motor. This discrete model can be viewed as a minimal ratchet model. We extend our previous work on this model, by further investigating the constraints imposed by the fluctuation theorem on the operation of a molecular motor far from equilibrium. In this work, we show the connections between different formulations of the fluctuation theorem. One formulation concerns the generating function of the currents while another one concerns the corresponding large deviation function, which we have calculated exactly for this model. A third formulation concerns the ratio of the probability of observing a velocity v to the same probability of observing a velocity -v . Finally, we show that all the formulations of the fluctuation theorem can be understood from the notion of entropy production.
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Affiliation(s)
- D Lacoste
- Laboratoire de Physico-Chimie Théorique, UMR 7083, ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France
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11
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Lau AWC. Fluctuation and correlation effects in a charged surface immersed in an electrolyte solution. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:011502. [PMID: 18351857 DOI: 10.1103/physreve.77.011502] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Indexed: 05/26/2023]
Abstract
We explore correlation and fluctuation effects in an overall neutral system consisting of a single homogeneously charged planar surface with both the counterions and coions distributed on both sides of the surface. Using a field-theoretic formulation, we compute the one-loop correction to the electrostatic potential, to the ion densities, to the surface tension, and to the surface free energy. From the asymptotic behavior of the electrostatic potential, we obtain an exact expression for the effective surface charge density, which can become negative, indicating charge inversion. Furthermore, we find that the ion distributions can be substantially different from the mean-field ion densities. In particular, the counterion density, at high couplings, develops a minimum at some intermediate distances, larger than the Gouy-Chapman length, away from the charged surface, whereas the coion density develops a maximum, whose values can be greater than the counterion density. Therefore, the coions develop a second layer. Moreover, the one-loop correction always lowers the electrostatic contributions to the surface tension and at high couplings, the surface tension may become negative.
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Affiliation(s)
- A W C Lau
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
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12
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Abstract
We investigate theoretically the violations of Einstein and Onsager relations and the thermodynamic efficiency for a single processive motor operating far from equilibrium using an extension of the two-state model introduced by Kafri et al. [Biophys. J. 86, 3373 (2004)10.1529/biophysj.103.036152]. With the aid of the Fluctuation Theorem, we analyze the general features of these violations and this efficiency and link them to mechanochemical couplings of motors. In particular, an analysis of the experimental data of kinesin using our framework leads to interesting predictions that may serve as a guide for future experiments.
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Affiliation(s)
- A W C Lau
- Department of Physics, Florida Atlantic University, 777 Glade Rd., Boca Raton, Florida 33431, USA
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13
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Chen DTN, Lau AWC, Hough LA, Islam MF, Goulian M, Lubensky TC, Yodh AG. Fluctuations and rheology in active bacterial suspensions. Phys Rev Lett 2007; 99:148302. [PMID: 17930729 DOI: 10.1103/physrevlett.99.148302] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Indexed: 05/18/2023]
Abstract
We probe nonequilibrium properties of an active bacterial bath through measurements of correlations of passive tracer particles and the response function of a driven, optically trapped tracer. These measurements demonstrate violation of the fluctuation-dissipation theorem and enable us to extract the power spectrum of the active stress fluctuations. In some cases, we observe 1/sqrt[omega] scaling in the noise spectrum which we show can be derived from a theoretical model incorporating coupled stress, orientation, and concentration fluctuations of the bacteria.
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Affiliation(s)
- D T N Chen
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
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Lau AWC, Lubensky TC. State-dependent diffusion: Thermodynamic consistency and its path integral formulation. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:011123. [PMID: 17677426 DOI: 10.1103/physreve.76.011123] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2007] [Indexed: 05/14/2023]
Abstract
The friction coefficient of a particle can depend on its position, as it does when the particle is near a wall. We formulate the dynamics of particles with such state-dependent friction coefficients in terms of a general Langevin equation with multiplicative noise, whose evaluation requires the introduction of specific rules. Two common conventions, the Ito and the Stratonovich, provide alternative rules for evaluation of the noise, but other conventions are possible. We show that the requirement that a particle's distribution function approach the Boltzmann distribution at long times dictates that a drift term must be added to the Langevin equation. This drift term is proportional to the derivative of the diffusion coefficient times a factor that depends on the convention used to define the multiplicative noise. We explore the consequences of this result in a number of examples with spatially varying diffusion coefficients. We also derive a path integral representation for arbitrary interpretation of the noise, and use it in a perturbative study of correlations in a simple system.
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Affiliation(s)
- A W C Lau
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
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15
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Abstract
We investigate the effect of counterion fluctuations in a single polyelectrolyte brush in the absence of added salt by systematically expanding the counterion free energy about Poisson-Boltzmann mean-field theory. We find that for strongly charged brushes, there is a collapse regime in which the brush height decreases with increasing charge on the polyelectrolyte chains. The transition to this collapsed regime is similar to the liquid-gas transition, which has a first-order line terminating at a critical point. We find that, for monovalent counterions, the transition is discontinuous in theta solvent, while for multivalent counterions, the transition is generally continuous. For collapsed brushes, the brush height is not independent of grafting density as it is for osmotic brushes, but scales linear with it.
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Affiliation(s)
- C D Santangelo
- Department of Physics, University of California, Santa Barbara, 93106, USA.
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Dogic Z, Zhang J, Lau AWC, Aranda-Espinoza H, Dalhaimer P, Discher DE, Janmey PA, Kamien RD, Lubensky TC, Yodh AG. Elongation and fluctuations of semiflexible polymers in a nematic solvent. Phys Rev Lett 2004; 92:125503. [PMID: 15089684 DOI: 10.1103/physrevlett.92.125503] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2003] [Indexed: 05/24/2023]
Abstract
We directly visualize single polymers with persistence lengths l(p), ranging from 0.05 to 16 microm, dissolved in the nematic phase of rodlike fd virus. Polymers with a sufficiently large persistence length undergo a coil-rod transition at the isotropic-nematic transition of the background solvent. We quantitatively analyze the transverse fluctuations of the semiflexible polymers and show that at long wavelengths they are driven by the fluctuating nematic background. We extract the Odijk deflection length and the elastic constant of the background nematic phase from the data.
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Affiliation(s)
- Z Dogic
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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17
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Lau AWC, Hoffman BD, Davies A, Crocker JC, Lubensky TC. Microrheology, stress fluctuations, and active behavior of living cells. Phys Rev Lett 2003; 91:198101. [PMID: 14611619 DOI: 10.1103/physrevlett.91.198101] [Citation(s) in RCA: 253] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2003] [Indexed: 05/18/2023]
Abstract
We report the first measurements of the intrinsic strain fluctuations of living cells using a recently developed tracer correlation technique along with a theoretical framework for interpreting such data in heterogeneous media with nonthermal driving. The fluctuations' spatial and temporal correlations indicate that the cytoskeleton can be treated as a course-grained continuum with power-law rheology, driven by a spatially random stress tensor field. Combined with recent cell rheology results, our data imply that intracellular stress fluctuations have a nearly 1/omega2 power spectrum, as expected for a continuum with a slowly evolving internal prestress.
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Affiliation(s)
- A W C Lau
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
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18
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Abstract
We consider an overall neutral system consisting of two similarly charged plates and their oppositely charged counterions and analyze the electrostatic interaction between the two surfaces beyond the mean-field Poisson-Boltzmann approximation. Our physical picture is based on the fluctuation-driven counterion condensation model, in which a fraction of the counterions is allowed to "condense" onto the charged plates. In addition, an expression for the pressure is derived, which includes fluctuation contributions of the whole system. We find that for sufficiently high surface charges, the distance at which the attraction, arising from charge fluctuations, starts to dominate can be large compared to the Gouy-Chapmann length. We also demonstrate that depending on the valency, the system may exhibit a first-order binding transition at short distances.
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Affiliation(s)
- A W C Lau
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
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19
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Lau AWC, Lin KH, Yodh AG. Entropic interactions in suspensions of semiflexible rods: short-range effects of flexibility. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 66:020401. [PMID: 12241139 DOI: 10.1103/physreve.66.020401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2002] [Indexed: 05/23/2023]
Abstract
We compute the entropic interactions between two colloidal spheres immersed in a dilute suspension of semiflexible rods. Our model treats the semiflexible rod as a bent rod at fixed angle, set by the rod contour and persistence lengths. The entropic forces arising from this additional rotational degree of freedom are captured quantitatively by the model, and account for observations at short range in a recent experiment. Global fits to the interaction potential data suggest the persistence length of the fd virus is about two to three times smaller than the commonly used value of 2.2 microm.
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Affiliation(s)
- A W C Lau
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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20
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Abstract
In this paper, we discuss the equilibrium phases and collapse transitions of a lyotropic nematic gel immersed in an isotropic solvent. A nematic gel consists of a cross-linked polymer network with rod-like molecules embedded in it. Upon decreasing the quality of the solvent, we find that a lyotropic nematic gel undergoes a discontinuous volume change accompanied by an isotropic-nematic transition. We also present phase diagrams that these systems may exhibit. In particular, we show that coexistence of two isotropic phases, of two nematic phases, or of an isotropic and a nematic phase can occur.
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Affiliation(s)
- D Lacoste
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA.
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21
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Lau AWC, Lukatsky DB, Pincus P, Safran SA. Charge fluctuations and counterion condensation. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:051502. [PMID: 12059559 DOI: 10.1103/physreve.65.051502] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2002] [Indexed: 05/23/2023]
Abstract
We predict a condensation phenomenon in an overall neutral system, consisting of a single charged plate and its oppositely charged counterions. Based on the "two-fluid" model, in which the counterions are divided into a "free" and a "condensed" fraction, we argue that for high surface charge, fluctuations can lead to a phase transition in which a large fraction of counterions is condensed. Furthermore, we show that depending on the valence, the condensation is either a first-order or a smooth transition.
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Affiliation(s)
- A W C Lau
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pensylvania 19104, USA
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